1. Field of the Invention
This invention relates to a slow-motion device of a magnetic recording and reproducing apparatus which performs slow-motion reproduction by feeding a magnetic tape intermittently.
2. Description of the Prior Art
In the past, various types of slow-motion reproduction schemes adapted for a magnetic recording and reproducing apparatus of helical scan type (hereinafter referred to as a VTR) have been proposed. In one known scheme, a magnetic tape is intermittently fed at intervals of one track or one pitch between tracks of the same azimuth, and still image reproduction is effected at every track to accomplish slow-motion reproduction.
In this known slow-motion reproduction scheme, however, it is general practice to feed the magnetic tape intermittently by using control signal information recorded on the same magnetic tape. More specifically, when still image reproduction at a track ends, the magnetic tape is driven until it stops at the time that the video head is placed in condition for scanning the succeeding track for reproduction thereat. And, the stoppage of the magnetic tape is effected by using a control signal reproduced from the information.
In general, however, individual VTRs suffer from slight irregularity in accuracies of fitting parts and consequently, the recording position of the control signal information with respect to tracks recording a video signal slightly differs from one VTR to another. Therefore, if the slow-motion reproduction is effected with the same VTR as that used for recording, no significant problem will arise but if effected with a VTR using a magnetic tape which is recorded by another VTR, there is a possibility that the magnetic tape is stopped with the video head incorrectly placed for scanning. Specifically, in the slow-motion reproduction wherein the video head is obliquely scanned along the track, it is necessary that a scanning error take place at the end of the track in order to prevent a noise bar due to the scanning error from being displayed on the reproduction screen and that the video head correctly scan the track at the central portion thereof. However, the aforementioned difference in the recording position of the control signal information leads to scanning errors which take place at portions of the track other than its end, resulting in a noise bar displayed on the reproduction screen.
A technical expedient for elimination of such problems has been known wherein a variable delay means such as a monostable multivibrator with a variable time constant is used to variably delay the control signal so as to artificially vary the recording position of the control signal information and the amount of delay of the control signal is adjusted by means of an adjusting means, while viewing the reproduction screen, such that any noise bar can be eliminated from the reproduction screen.
However, the adjusting means is operated by the user, who is disadvantageously forced to participate in very troublesome work. Moreover, the provision of the adjusting means in a VTR results in complexity of the construction and expensiveness of the VTR.